Method for producing permanent integral connections of oxide-dispersed (ODS) metallic materials or components of oxide-dispersed (ODS) metallic materials by welding

ABSTRACT

A method for producing permanent integral connections of oxide-dispersed metallic materials by welding. The materials or components to be connected are overlapped to form an overlapping region in a joining region of the overlapping region. The materials or components are heated below the melting temperatures of the materials and are welded to at least partially form a diffusion bond by a welding method. A noble metal foil may be between the components to be connected. The diffusion bond is heated subsequently to a temperature below the melting temperature of the materials or components and the bond is mechanically recompacted by hammering.

BACKGROUND OF THE INVENTION

The invention relates to a method for producing permanent integralconnections of oxide-dispersed (ODS) metallic materials, in particularfor producing integral connections of components ofoxide-dispersion-strengthened noble-metal alloys, specifically withsuccessive heating steps and mechanically shaping the bond at theconnection.

It is known in the production of special types of glass to usestructural elements encased in noble metal, for example stirrers,channels, feeder heads, for homogenizing or transporting the glass melt.The noble-metal alloys used are usually platinum base alloys withalloying additions of rhodium, iridium or gold. If very high componentstrengths are required on account of mechanical and/or thermal loadsimposed by the glass melt, oxide-dispersion-strengthened platinum basealloys are increasingly used, since they are characterized by a greaterthermal, mechanical and chemical load-bearing capacity than standardalloys. Oxide-dispersed alloys, referred to hereafter as ODS alloys, aredistinguished by a very homogeneous microstructure. ODS noble-metalalloys based on PtRh10, PtAu5 or pure Pt, which are used for producingcomponents in the glass industry, additionally have a much lowertendency for coarse grains to form at high temperatures, allowing themechanical properties to be positively influenced. Apart from the choiceof suitable material, however, the production, in particular shaping, ofthe structural elements encased in noble metal also plays an importantpart in determining the strength. They are generally produced fromsemifinished products, i.e. metal sheets or sheet-metal elements arejoined together to give the required geometry. This connection isgenerally produced by fusion welding of the individual semifinishedproducts. In this case, the joints of the components to be connected toone another and, if appropriate, additional material of the same typeare transformed into the molten state by heat being supplied and theyare fused together. The heat of fusion may in this case be generated byan electric arc or an ignited gas-oxygen mixture. If, however,structural elements joined in such away are exposed to very hightemperatures, for example above 1200° C., the welded seam often formsthe weak point of the overall material bond. Inhomogeneities in thewelded seam and changes in the microstructure in the heat-affected zonehave been determined as the cause. Particularly longitudinal weldedseams in cylindrical components, such as pipes for example, areparticularly at risk because of the stresses acting that areapproximately twice as high as in the case of circumferential weldedseams, with the result that the seams often fail and tear apart. Whenknown welding methods are used, such as for example tungsten-inert gaswelding (TIG welding), plasma welding, laser or autogenous welding,melting of the alloy is brought about. While only very small losses instrength in the welded seam are to be observed during the melting ofclassic substitutional solid solution alloys as a result ofrecrystallization during use above 1200° C., the melting whenoxide-dispersion-strengthened alloys are welded leads to coagulation andfloating of a large part of the disperoids, typically of ZrO₂ and/orY₂O₃, in the melt. A coarse-grained solidification structure is producedin the welded seam. The strengthening effect of the dispersoids in thewelded seam is consequently negated. The load-bearing capacity andservice life of a structural element joined together in such a way thenfalls to the level of structural elements joined from standard alloys.Measures to avoid this disadvantage are already known from thepublications JP 5212577 A and EP 0320877 B1. In the case of the methodsdisclosed therein, a fusion-welded seam on ODS sheets is subsequentlycovered with a Pt-ODS sheet and pressed into the seam by hammering athigh temperatures. This measure brings about an increase in the finenessof the grain size distribution on the surface of the welded seam throughthe sheet and consequently a reduction in the probability of crackformation on the surface. A further possible way of compensating for thedecrease in strength in the welded seam has been seen in forming theconnection by means of flanged seams. However, these require undesiredthickenings of the material in the joining region, which have theconsequence when these components are heated in the direct currentflow—for example for the purpose of heating the glass melts passedthrough structural elements joined in such a way—of producingdifferences in temperature at the seam, which in glass production may inturn lead to considerable glass defects. Furthermore, satisfactorybeading of these thickened welded seams is possible only to a restrictedextent. Alternatively, therefore, recourse is made to integralconnections formed by means of hammer-welded seams. However, connectionsof this type are subject to very great variations in quality. Toeliminate these variations, an extremely great expenditure is requiredfor the preparation of the welded seam and very exact control of theprocess parameters during the welding. In the case of this method,uniform heating of the materials to be joined, in particular metalsheets, during hammering proves to be difficult. When doing so, it isoften scarcely possible to heat the lower sheet in the welding positionadequately with the torch to achieve a good adhesive effect during thehammering. The method is consequently very laborious, does notnecessarily lead to an optimum result and is very cost-intensive.Furthermore, there is a fundamental problem when fabricatinghammer-welded seams, in that there is a low adhesive tendency of thematerial during the hammering in the case of alloys with a rhodiumcontent >4% by weight and in general in the case of ODS alloys. Theoxides already contained in the ODS material or the oxides formingduring the hammering, mainly rhodium oxide, significantly reduce theadhesive bonding of the two components, in particular metal sheets. Thepoor adhesive bonding has the effect of increasing the productionexpenditure considerably, but also at the same time of increasing therisk of no adequate bond being achieved any longer in certain regions ofthe joining region in the seam.

As a further possible way of producing welded connections ofoxide-dispersion-strengthened alloys with high strength, welding withalloying additions containing zirconium and/or yttrium was considered.These alloying constituents should be separated during use attemperatures above 1200° C. by internal oxidation of the dispersoids inthe material and consequently a strengthening effect achieved in thewelded seam. In practice, however, it has been found that this methodproduces only inadequate results, since, during the separation of thedispersoids, the increase in the grain size also occurs at the sametime. Consequently, a coarse-grained microstructure in which only a fewdispersoids are separated, and the mechanical properties of which aretherefore inadequate, often forms very quickly. Such a method forproducing pipes from ODS noble metals is described in DE 197 14 365 A1.In the case of this method, as well as the heat treatment, additionalrolling is required, whereby the working becomes very protracted andlaborious.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of providing a method forwelding oxide-dispersed (ODS) metallic materials for producing aconnection of components of oxide-dispersion-strengthened alloys whichsatisfies the increased requirements of structural elements formed fromthem during use for glass production, i.e. for providing a connectionwhich is distinguished by high strength and thermal load-bearingcapacity and under high temperatures does not lead to undesired changesin microstructure, which have an adverse influence on the glass meltsflowing around or through these structural elements, which results inglass defects.

For the terms used hereafter for explanation, the following definitionsare taken as a basis:

-   -   joining region the region between two materials or components        which is characterized by the integral connection    -   overlapping region the region which is characterized by the        contact or lying one on top of the other of the materials or        components to be connected to one another or in the case where        there is no direct contact of the desired arrangement of the        latter with integral connection in relation to one another        during positioning for the welding operation    -   joints surface-area segments or regions of the surface areas        facing one another and lying against one another for the welding        operation on positioned oxide-dispersion-strengthened components        which are connected to one another by means of the integral bond    -   heat-affected zone region in which the microstructure of the        materials or components to be connected to one another is        influenced and changed when heat is supplied    -   advancing direction direction of the movement of the welding        device or of the positioned materials or components.

According to the invention, during the method for producing permanentintegral connections of components of oxide-dispersed (ODS) metallicmaterials, the welding of the individual materials is respectivelyperformed below their melting temperature, with at least partialformation of a diffusion bond in the joining region. In a second methodstep, the diffusion bond, preferably the entire joining region, isheated to a temperature which likewise lies below the meltingtemperature of the materials or components to be connected to oneanother and, at this temperature, is mechanically recompacted,preferably hammered. Depending on the arrangement in relation to oneanother before the welding operation, the two materials to be connectedto one another in this case define the joints, the latter generally alsodefining the joining region, i.e. the region in which the desiredconnection between the two is to be produced. According to theinvention, consequently a permanent integral connection of components ofoxide-dispersed (ODS) metallic materials is provided by arranging forthe production of a diffusion-welded bond to be performed before themechanical recompaction under heat. The diffusion bond permits good heatintroduction into the two components to be connected to one another, sothat a very high residual strength remains in the joining zone after thesubsequent mechanical recompaction, and consequently a material bondwhich can be subjected to high loading is obtained in this region. As aresult of the shaping of the bond by the subsequent mechanicalrecompaction, there is no abrupt transition between the two materialsbut a continuous transition. This continuous transition is characterizedby very good thermomechanical properties, which make it possible forsuch connections of oxide-dispersed metallic materials also to be usedat very high temperatures, for example at > or =1400° C.

For producing the diffusion bond, the melting temperature of thematerial which has the lower value is set as the limiting temperature.According to a particularly advantageous refinement, in this case amelting temperature in the range including 0.6 to 0.9 times, preferably0.7 to 0.9 times, the amount of the melting temperature is chosen. As aresult, only little melting is achieved. The diffusion bond is therebyproduced during the diffusion welding by matching forming of the joiningfaces and diffusion of the atoms via the abutting faces of thecomponents or materials to be connected to one another in the joiningregion. According to a particularly advantageous refinement, thisprocess takes place while a constant pressure is being applied in thejoining region, in order to press together the components which are tobe connected, although without any plastic deformation, or only verylittle plastic deformation, in the single-digit percentage range.

The following welding methods are used here, notable for reduced energyinput, which keeps down as much as possible the melting of thecomponents or materials to be connected to one another:

-   1. fusion-welding method-   2. pressure-welding method

In the first-mentioned case, the fusion-welding method, the joints ofthe materials to be connected and, if appropriate, when using anaddition of the same type, said addition are transformed partially intothe molten state by heat being supplied, as a result of the reducedenergy input. This means that the materials to be connected to oneanother are not completely melted during welding and a diffusion bond isat least partially produced in the joining region. The completeconnection in the joining region then takes place by the subsequentworking operation of mechanical recompaction under heat, generallyhammering. A combination of a fusion-welding method in the form of whatis known as the tungsten-inert-gas welding method (TIG welding) and ahammer-welded seam has been determined as particularly advantageous forimproving the thermomechanical strength in the joining zone. In thiscase, a significantly reduced energy input is used during the TIGwelding, the two materials or components which are to be welded notmelting completely during welding. The two materials are then completelywelded to one another in the joining region by the subsequent hothammering, good heat introduction into the two components to beconnected to one another being achieved through the welded seam. Sincethe melting zone of the TIG seam is only about 15% to 25% of thethickness of one component and the melting zone is deformed considerablyduring the hammering, a very high residual strength remains in thejoining zone.

In the case of the pressure-welding method, the joints of the materialswhich are to be connected are locally brought into a kneadable state byheat being supplied and are plastically unified by pressure. The heat isusually generated by electrical energy, in particular resistanceheating. Other forms of energy are possible. If a lower energy input isused here, too, complete melting does not take place. The actual weldingis then performed by the pressure being applied, which leads to plasticunification.

Characteristic method parameters for producing the diffusion bond are inthis case the welding temperature, the contact pressure and the weldingtime, which is characterized by the time period of local exposure totemperature and pressure in the joining region. Since the mass transferjust by diffusion generally requires pure, oxide-free surfaces, work ispreferably carried out in a vacuum and inert-gas atmosphere.

The mechanical recompaction is performed at temperatures which likewiselie below the melting temperature of the components to be connected toone another of oxide-dispersed (ODS) metallic materials, by impactloading, preferably constant exposure to impact, of the diffusion bond,in particular by hammering. The energy input takes place for exampledirectly by electrical current flow. Other possibilities areconceivable. On account of the overlapping, the effect does not takeplace directly but onto the diffusion bond via the components. Thehammering may in this case be performed on one side or else on bothsides. In the first-mentioned case, the impact loading is exerted on thecomponent in the joining region, while the other, second component issupported against a fixed stop, which produces a counterforce to theforce applied by the impact loading. In the other case, the exposure toimpact takes place simultaneously on both sides.

With the solution according to the invention, it is possible to providean integral connection between oxide-dispersed metallic materials whichis characterized in the joining region by high strength and goodthermomechanical properties and in this respect does not differ from thecomponents to be connected. There is no material weakness to be found inthe joining region, with the result that crack formations can bevirtually ruled out here. Furthermore, this type of connection producesa transition between the two components to be connected for which nojoining zone is evident in the metallographic transverse section.

With respect to the arrangement and types of joint, there are a numberof possibilities:

lap joint, i.e. the parts overlap one another

parallel joint, i.e. the parts lie against one another over a broadsurface area

The materials are in this case preferably arranged for joining such thatthey overlap in such a way that they have an overlapping region whichcorresponds to three to six times the sheet thickness. The contact areasin the overlapping region may be planar or else formed in a beveledmanner. This arrangement is possible both for the fusion-welded variantand the pressure-welded variant for achieving the diffusion bond.

With the solution according to the invention, material bonds ofoxide-dispersed (ODS) metallic materials or between components of thesematerials can be produced in any desired number n, preferably from twoor three components. They are then arranged overlapping one another inthe joining region. In a perpendicular sectional plane through theoverlapping region, the number of parallel joining regions between whichthere are in each case two components contacting one another is thenequal to (n−1).

The production of the diffusion bond by pressure welding furthermorepreferably comprises that the oxide-dispersion-strengthened noble-metalalloy components are arranged and positioned overlapping one another inthe joining region to form an overlapping region and the joints of theoxide-dispersion-strengthened noble-metal alloy components produced bythe overlapping arrangement are locally brought into the flowable stateone after the other progressively in the advancing direction of thewelding device or of the components to be connected to one another byheat being uniformly supplied on both sides of the overlapping region inthe heat-affected zone and plastically unified under pressure. Thedistance between two neighboring welding points produced when theindividual joints are connected is less, considered in the advancingdirection, than the dimension of a welding point in this direction.Consequently, the connection by means of a pressure-welding method takesplace over a continuous welded seam, whereby very homogeneousmicrostructures can be achieved in the region of the heat-affected zone.The connection produced in this way is then characterized by highservice lives.

The additional optimum matching of the process parameters to oneanother—rate of advancement of the components or of the welding device,contact pressure and heat supplied—allows the melting to be controlledin such a way that it occurs only at the areas of contact, i.e. thejoints, between the two components. Complete melting of the welded-seamregion can consequently be avoided. A small depth of the melting zone inthis case advantageously does not bring about any change in thefine-grained microstructure in the heat-affected zone of theoxide-dispersion-strengthened noble-metal alloy components.

With a very high chosen density of the welding points, considered in theadvancing direction, a seam with a virtually uniform seam thickness canbe achieved over the extent in the advancing direction. Such connectionsare then particularly suitable for the fabrication of structuralelements encased in noble metal from a number of individual semifinishedproducts of oxide-dispersion-strengthened noble-metal alloys, thegeometry of which is determined by the connection of these componentsand which can be integrated into processing processes as a tool orguiding means which expose the structural element to high thermal andmechanical loads with at the same time the required homogeneous behaviorof the structural element—including the material connection. Suchstructural elements are used for example in glass production for thepurpose of influencing, in particular homogenizing and guiding, glassmelts as stirrers, channels or feeder heads.

Straight-line spot welding or seam-welding methods are preferably usedas the pressure-welding method, the arrangement of the seam connections,considered in the advancing direction, taking place in one row or tworows, i.e., when the components take the form of metal sheets, one seamor two parallel seams are arranged in the advancing direction. Suchmaterial bonds are distinguished by increased strength.

The supply of heat can be ensured in this case by means of differentforms of energy. Electrical energy or ultrasound are preferably used.According to a particularly advantageous refinement of the methodaccording to the invention, a resistance welding method is used as thewelding method, in which the required heat of fusion is induced by meansof at least one welding electrode which can be connected to at least onepower source, is arranged on both sides of the overlapping region andacts on the respective component, during the brief action of a currenton the welding electrode as a result of the high transition resistanceat the component. The required contact pressure is in this case producedby means of the electrodes. The melting depth on theoxide-dispersion-strengthened noble-metal alloy components is in thismethod controllable as a function of the current intensity and/or therate of advancement and/or the contact pressure.

Preferably, a roller seam-welding method is used as the resistancewelding method, welding electrodes lying opposite one another in theform of rolling electrodes being arranged on both sides of theoverlapping region. These rolling electrodes are rotatably mounted andat least one of the two can be driven, so that the rolling movement canbe used for advancing the components. The rolling electrodessimultaneously also exert the pressure on the components. According to aparticularly advantageous refinement, they may also be beveled. Thebevel then has a width which corresponds to 3 to 7 times the amount ofthe thickness of the components. With this solution, very high weldingseam densities can be achieved with minimal expenditure, reflected in aseam with a uniform seam thickness over the entire region of the extentof the seam in the advancing direction. For changing the contactpressure, the rolling electrodes are mounted displaceably with respectto the components.

According to an advantageous configuration, the electrodes are cooled,preferably water-cooled.

To achieve material bonds of a number of components with a wallthickness which is as uniform as possible, i.e. equal wall thicknessesin the joining region and outside, according to a particularlyadvantageous further development the oxide-dispersion-strengthenednoble-metal alloy components are respectively beveled in the joiningregion and the components are arranged overlapping such that they lieagainst one another at the beveled faces produced in this way. As aresult, the components can be arranged in one plane, the wall thicknessof the material bonds produced from the two components by welding at thewelded seam or in the direct vicinity of the welded seam being retainedwith respect to the wall thickness of the individual component. Themechanical recompaction then also does not lead to thickening in thejoining region. Such connections are then particularly suitable forjoining together components to form structural elements which are usedin processes for which, for example, a uniform heat transmissionbehavior over the entire extent of the material bond is of specialsignificance.

To achieve an overlapping region which is as large as possible, thelength of the beveled faces, considered in cross section through acomponent, is a multiple of the thickness of the component, inparticular at least 2 to 5 times.

To avoid displacement or slipping of the components placed one on top ofthe other in the welding position under the influence of the contactpressure in the case of beveled components, according to an advantageousfurther development the beveled faces are provided in the joiningregion, preferably in the entire overlapping region, with an increasedsurface roughness. This may be characterized for example by at least oneof the parameters stated below:

-   -   ten-point height R_(z) (according to ISO=arithmetic mean of the        absolute amounts of the five respectively greatest profile peak        heights and profile valley heights)    -   arithmetic mean roughness value R_(a) (arithmetic mean value of        the absolute amounts of the profile deviations within the        roughness reference zone)    -   maximum profile valley depth R_(m) (distance of the deepest        profile from the center line)    -   maximum profile height R_(y)=R_(t) (distance between the line of        the profile cusps and the profile valleys R_(y)=R_(p)+R_(m))    -   maximum profile cusp height R_(p) (distance of the highest point        of the profile from the center line within the reference zone)    -   /averaged roughness depth R_(z)/(mean value of the roughness        coefficient of five reference zones within an evaluation length)    -   The averaged roughness depth of the roughened regions of the        surface area is 10 to 100 times the averaged roughness depth of        the components to be connected to one another.        Typical roughened surfaces have a roughness of between R_(z)˜40        mm and R_(z)˜120 mm, inclusive.

The required roughness may in this case already take place when bevelingby separating with defined cutting or else by later surface working byseparating with undefined cutting, for example grinding. According to aparticularly advantageous configuration, the components are specificallyroughened in the beveled region by means of an embossing roller. Theroughening reliably prevents the components from sliding apart, whichleads to greater accuracy of the geometry of the welded seam andconsequently of the material bond or the structural element produced.Furthermore, the welded seams produced are characterized by a greaterload-bearing capacity than welded seams on smooth surface areas, sincethe roughening makes it possible to keep better control over the weldingparameters, since the contact area that is decisive for the currenttransfer by the pressing of the roughened regions into one another ismade more uniform by the selective roughening.

A further major advantage of a material bond produced according to theinvention with joining faces beveled in the joining region is that theoverall welded material bond can also be subjected to further workingsteps, in which for example beads which run perpendicularly to thewelded seam can be formed both into the components and in the joiningregion.

According to a particularly advantageous further development of thesolution according to the invention, irrespective of the chosen methodfor producing the diffusion bond, it is envisaged to use a weldingfiller. This is arranged in the joining region between the two materialsor components of oxide-dispersed metallic materials which are to bejoined to one another. The welding filler may in this case take the formof a separate element or else a coating on at least one of the mutuallyfacing joining areas in the joining region. Ductile fusion-alloyedalloys, for example PtAu5, PtIr1, pure Pt, but also stronger alloys, forexample PtRh5, PtRh10, PtIr3, are suitable in particular here as weldingfillers.

The welding filler allows a much better bond to be achieved between thetwo materials to be connected to one another, since the adhesivetendency between the two materials is significantly increased, whichconsiderably reduces the fabrication expenditure. Furthermore, thethermal and mechanical load-bearing capacity of the joining zones isconsiderably increased. The effect is based on the fact that thesuperficially formed oxides in the overlapping zones are pressed intothe ductile material of the welding filler, whereby a solid bond isobtained between the two materials.

Preferably, since it can be realized with little expenditure, at leastone noble metal foil is inserted between the materials to be connectedto one another. Said foil is preferably characterized by a thickness of20 mm to 200 mm, inclusive. Typically, the thickness of the noble metalfoil is 30 mm to 150 mm, in exceptional cases up to 250 mm. Thesubsequent hammering at high temperatures then allows the two materialsto be joined together very easily. Micrographs through the hammeredjoining zone show that a welded seam in which the original foil makes upless than 30 mm of the thickness is formed. The diffusion processesduring the actual welding have the effect that a material bond which canwithstand great loading is then produced in this region. Instead ofrolled platinum foils, gold leaf may also be used. The foils themselvesmay consist entirely of the alloys mentioned or else merely be providedwith a correspondingly thick coating of them, the contact with thecomponents to be connected taking place via the coating. Furthermore,there is the possibility of using not just a single foil but a foillaminate, i.e. the n+1 foils can be connected to one another, with n≧1.

According to an alternative configuration, instead of the insertion of afoil, the respective contact zone of the materials to be connected toone another may also be coated in a foil-welding manner in theoverlapping region with a thin noble metal layer, in analogy with thefoil, for example by platinum alloys. This coating may for example beelectrodeposited or else applied by currentless deposition. Alsoconceivable is a coating by means of a thermal spraying operation. Inthis case, layers with a thickness of 30 mm to 80 mm, inclusive, arepreferably applied.

The production of hammer-welded seams by mechanical recompaction byhammering with foils as an intermediate layer is particularly simple ifa pressure-welding method in the form of a roller seam-welding method,as already described, is additionally used for producing the diffusionbond. In this case, the foil is inserted between the two components orthe materials to be connected to one another. The two components arefirmly connected to one another by means of the roller seam welding. Thedecisive advantage is that no impurity in the form of oxides can getbetween the foil and the components. Impurities in the form of oxidesalways mean that the welded seam is weakened and can lead to failure ofthe seam under loading. Only in the subsequent working step is the jointthen hot-hammered. A further additional improvement in the roller seamwelding can be further achieved by the use of tungsten electrodes andmolybdenum electrodes. This is so because sticking of the electrodes tothe noble metal sheets to be welded is very often encountered whenelectrodes made of copper or its alloys are used, greatly restrictingthe choice of welding parameters. With the preferred electrode material,the welding parameters, in particular the current intensity and contactpressure, can be varied over a very wide range, with the result that nomelting is achieved at the contact locations between the materials to bejoined to one another during the welding, but an adequate bond cannevertheless be achieved. This bond is a pure diffusion bond. The lowertendency to stick in the case of molybdenum or tungsten is caused by theformation of volatile oxides which evaporate during the welding at hightemperatures.

One particular advantage in the case of the method for roller seamwelding is, furthermore, that even metal sheets or foils with a very lowwall thickness can be welded to one another. Following this, only verylittle hammering is necessary. The method described is consequentlypreferably able to be used for welding relatively thin sheets, inparticular of thicknesses of 50 mm to about 5 mm, inclusive, inexceptional cases even greater.

A further advantage is that ODS alloys based on PtRh10 can be joineddirectly to melt-metallurgically produced standard alloys (Pt—Rh, Pt—Auand Pt—Ir). As a result of the shaping of the seam during forging, thereis no abrupt transition between the two materials, but rather acontinuous transition takes place. This continuous material transitionin turn has advantages with regard to the thermomechanical properties.

In the production of the welded seam generally with a method accordingto the invention and corresponding positioning of the welding device,the components can be characterized with regard to their position by thefollowing welding position:

-   -   combined gravity and overhead position, i.e. the components are        aligned in a horizontal plane and the supply of heat required        for the welding method and the pressure required for the plastic        deformation take place perpendicularly, i.e. in the vertical        direction in relation to the structural elements to be joined,        both from above and from below    -   combined horizontal and half-overhead position, i.e. the        components to be joined are aligned at an angle to the        horizontal, the welding device correspondingly perpendicular to        the latter    -   horizontal-vertical position, i.e. the structural elements to be        joined are arranged in the vertical direction and the supply of        heat required for the welding method and the pressure required        for the plastic deformation take place perpendicularly, i.e. in        the horizontal direction onto the structural elements to be        joined.

With respect to the application of the method according to theinvention, there are no restrictions on the configuration of theindividual components. In the case of the oxide-dispersion-strengthenednoble-metal alloy components, they may be both planar and shaped sheetmetal elements or hollow bodies, such as pipes for example.

With the method according to the invention,oxide-dispersion-strengthened noble-metal alloys which contain zirconiumoxide and/or yttrium oxide as a fine-grained stabilizer can be weldedwell. The method is advantageously suitable furthermore for the weldingof oxide-dispersion-strengthened platinum base alloys, i.e. pureplatinum, platinum-rhodium, platinum-gold and platinum-iridium. In thiscase, materials of the same composition but also components of differentmaterials can be welded to one another.

Further according to the invention, n oxide-dispersion-strengthenedmaterials can be connected at a number of the joining regions which areparallel in a perpendicular sectional plane through the overlappingregions and between two of the components by setting the number ofjoining regions to be equal to n−1.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the invention are explained below on thebasis of Figures, in which specifically:

FIGS. 1 a and 1 b illustrate on the basis of two sectionalrepresentations through a welding device in a schematically greatlysimplified representation the basic principle of a particularlyadvantageous embodiment of the first method step for producing adiffusion bond of the method according to the invention by a rollerseam-welding method, the components to be connected to one another beingbeveled in the joining region;

FIG. 1 c illustrates a further development according to FIGS. 1 a and 1b with a noble metal foil inserted between in the joining region of thetwo structural elements to be connected to one another;

FIG. 1 d illustrates in a schematically greatly simplifiedrepresentation the basic principle of the second method step in the formof the mechanical recompaction of the diffusion bond according to FIGS.1 a–1 c by hammering;

FIGS. 2 a and 2 b show on the basis of two sectional representationsaccording to FIGS. 1 a and 1 b the method for producing a diffusion bondwith components arranged in two planes;

FIG. 2 c illustrates on the basis of the configuration according to FIG.2 a the production of a diffusion bond with the aid of a welding fillerin the form of a coating in the joining region;

FIG. 3 a illustrates in a schematically simplified representation afurther possible way of achieving a diffusion bond by means of amodified fusion-welding method;

FIG. 3 b illustrates in a schematically simplified representation thecombination of a welding method according to FIG. 3 a with downstream orsubsequent mechanical compaction at an elevated temperature on the basisof the connection of two oxide-dispersed (ODS) metallic materials;

FIG. 4 a illustrates a metallographic transverse section through anintegral connection by roller seam welding and subsequent recompaction,without a welding filler;

FIG. 4 b illustrates a metallographic transverse section through anintegral connection by means of roller seam welding and hammer weldingwith a welding filler in the form of a noble metal foil.

PREFERRED EMBODIMENTS OF THE INVENTION

FIGS. 1 a and 1 b illustrate in a schematically simplifiedrepresentation on the basis of two sectional representations through awelding device 1 the basic principle of the first method step of themethod according to the invention for realizing an integral connection 2which can be subjected to thermal and mechanical loading of twocomponents 3 and 4, in particular two oxide-dispersed (ODS) metallicmaterials or of two components of oxide-dispersion-strengthenednoble-metal alloys, the production of a diffusion bond 25, focusing hereon a particularly advantageous embodiment of the method step forproducing the diffusion bond 25. FIG. 1 a thereby illustrates asectional view in the advancing direction of the two components 3 and 4through the latter, FIG. 1 b illustrates a sectional view transverselyto the advancing direction.

The arrangement of the two components 3 and 4 to be welded in thewelding position takes place according to a particularly advantageousembodiment in a common plane E1, the two components 3 and 4 beingarranged such that they overlap in the joining region 5. Joining region5 is understood here as meaning the region which is characterized by thedirect integral connection of the two components 3 and 4. The axialextent I of the overlap defines an overlapping region 6. In this case,the two components 3 and 4 have in a particularly advantageous way, atleast in the overlapping region 6, in each case a bevel 7 and 8, whichin the welding position of the two components 3 and 4 is aligned in sucha way that the beveled faces 9 of the bevel 7 and 10 of the bevel 8,face one another and lie against one another. To avoid slipping of thecomponents 3 and 4 in the welding position with respect to one another,at least the surface-area regions of the beveled faces 9 and 10 whichare integrally connected to one another under the effect of heat andforce are provided with an increased surface roughness, preferably theentire beveled faces 9 and 10. The surface roughness may in this case becharacterized for example by the mean surface roughness or some othercharacteristic roughness value. The desired roughening of the surfacemay already be produced by the fabrication, i.e. when the bevel isproduced, or else by subsequent surface working of the beveled face. Theactual selection is at the discretion of the relevant person skilled inthe art.

The chosen method in the case represented is a resistance weldingmethod, preferably a resistance roller seam-welding method, in which thejoints obtained by the overlapping arrangement of theoxide-dispersion-strengthened noble-metal alloy components 3 and 4 arelocally brought into the kneadable state one after the otherprogressively in the advancing direction of the components 3 and 4 to beconnected to one another by heat being uniformly supplied on both sidesof the overlapping region 6 in the heat-affected zone WEZ andplastically unified under pressure, preferably constant pressure, thedistance between two neighboring welding points produced when theindividual joints are connected being less, considered in the advancingdirection, than the dimension of a welding point in this direction.According to the invention, the heating in the heat-affected zone isonly performed, however, to a temperature which lies below the meltingtemperature of the components 3 and 4 to be welded, to one another,preferably corresponds to 0.7 to 0.9 times the amount of the meltingtemperature of the component with the lower melting temperature. Thewelding device 1 comprises for this purpose at least two weldingelectrodes 11 and 12, which are assigned the two components 3 and 4 inthe overlapping region 6, opposite one another, respectively act on acomponent 3 or 4, can be supplied with power via an energy source 13 andin the case represented are rolling electrode. Both are rotatablymounted and preferably at least one of the two can be driven. Therequired heat of fusion is induced during the brief action of a currenton the welding electrode 11 and 12 us a result of the high transitionresistance at the component 4 and 3. The required contact pressure is inthis case produced by means of the electrodes 11 and 12. When configuredas rolling electrodes, they serve for transporting the components 3 and4 in the advancing direction. The melting depth on theoxide-dispersion-strengthened noble-metal alloy components 3 and 4, inparticular at the beveled faces 9 and 10 coming into contact with oneanother, is in this method controllable as a function of the currentintensity and/or the rate of advancement and/or the contact pressure p.There maybe provided for this purpose a control device 14, which isrepresented here only very schematically and in each case is coupled tothe actuating devices for influencing these parameters. The contactpressure p is realized by variation of the pressing force F, for exampleby means of the displaceability of the welding electrodes 11 and 12 withrespect to the components to be connected to one another, illustratedhere by a double-headed arrow at the mounting 15 of the weldingelectrode 11. The rate of advancement can be influenced by changing therotational speed Δn of the rolling electrodes 11 and 12. Furthermore,the current intensity can be changed by ΔI. According to the invention,the energy input takes place via the welding electrodes 11 and 12 insuch a way that complete melting does not take place, but rather aconnection by diffusion is realized. A material which does not reactwith the components 3 and 4 to be joined is preferably chosen as theelectrode material for the welding electrodes 11 and 12. Therefore,electrodes made of molybdenum, tungsten or their alloys are preferablyused.

In the sectional representation I—I according to FIG. 1 b, it is evidentthat the distance a between two neighboring welding points, here forexample 25,11, 25,12, 25.13 and 25.14, produced when the individualjoints are connected is less, considered in the advancing direction,than the dimensional of a welding point 25.13 in this direction. With avery high welding point density, and consequently seam density, theintegral connection 25 can be produced in the form of a seam 16 withvirtually uniform seam thickness d over the extent in the advancingdirection.

In the case of the configuration represented in FIGS. 1 a and 1 b, theseam is for example of a single row.

FIG. 1 c illustrates a further development according to FIG. 1 a, inwhich a welding filler 26 in the form of a noble metal foil 17 isprovided in the overlapping region 6 between the beveled faces 9 and 10.The thickness of the foil 17 is preferably 30 mm to 150 mm, inclusive.Suitable in particular as this foil are ductile fusion-alloyed alloys,for example PtAu5, PtIr1, pure Pt, but also stronger alloys, for examplePtRh5, PtRh10, PtIr3. The advantage is that, during the roller seamwelding operation, no impurities can get between the foil 17 and thecomponents 3 and 4.

The foil 17 is dimensioned in such a way that it preferably extends overthe entire joining region 5 both in the advancing direction andtransversely to the advancing direction, it being characterized by atleast a subregion, preferably the entire region of the overlappingregion 6.

Reproduced in the schematically simplified representation in FIG. 1 d isthe basic principle of the second method step, the mechanicalrecompaction at higher temperature for a diffusion bond 25 according toFIGS. 1 a to 1 c, resulting in the integral connection 2. Provided inthis respect is a device 18, which applies local impact loading to thediffusion bond 25 in the joining region 5 and, furthermore, a device 19,which heats the joining region to a very high temperature, which howeveris likewise below the melting temperature of the materials or components3 and 4 of oxide-dispersed metallic materials to be connected to oneanother. This may take place directly after the roller seam-weldingmethod, i.e. in a common device, the expenditure in terms of the devicein this case being very high and can be realized only by means ofspecial devices. This means that the components 3 and 4 to be connectedto one another are then fed in the advancing direction to the device 19and the device 18. The device 19 and the device 18 may in this caselikewise be spatially combined or else arranged one behind the other.Preferably, however, the second method step of mechanical recompactionis performed at a separate place and at a separate time than the first.In this case, the components 3 and 4 are first connected by means of theroller seam-welding method in the welding device 1. After passing thewelding device 1, the diffusion bonds 25 produced in this way canfirstly be buffer-stored and are then subjected in a further, secondmethod step, i.e. after a time interval with respect to the weldingoperation, to the mechanical finishing, in particular recompaction. Thechoice of the procedure is then at the discretion of the relevant personskilled in the art.

The heating for the purpose of recompaction is preferably performed bydirect current flow. The device 19 is then to be designed in thisrespect. The recompaction may in this case be performed on one side, asrepresented. In this case, the device 18 comprises a first subdevice,which is mounted movably with respect to the components 3 and 4connected by means of diffusion bond 25, and applies a thrust or impactloading to the latter. As this happens, the second subdevice supportsthe components 3 and 4. It is, however, also conceivable to achieve themechanical recompaction by applying impact loading on both sides of thediffusion bond 25.

FIGS. 2 a and 2 b illustrate a simplified configuration of the methodaccording to the invention for the pressure welding ofoxide-dispersion-strengthened noble-metal alloy components 3.2 and 4.2according to FIGS. 1 a and 1 b, dispensing with an arrangement of thecomponents 3.2 and 4.2 in one plane E1. The components 3.2 and 4.2 arearranged overlapping one another in two planes E1 and E2, i.e.dispensing with the respective bevels 7 and 8. The overlapping of thetwo in this case determines the overlapping region 6.2. The basic setupof the welding device 1.2 corresponds to that described in FIG. 1 a, forwhich reason the same designations awe used for the same elements. Withrespect to the operating principle of the welding device 1.2, referencecan be made to the description relating to FIG. 1 a. FIG. 2 billustrates a sectional representation II—II according to FIG. 2 a.Here, too, it is evident that the distance a₂ between two neighboringwelding points, here for example 25.21, 25.22, 25.23 and 25.24, producedwhen the individual joints are connected is less, considered in theadvancing direction, than the dimension a1 ₂ of a welding point 25.23 inthis direction. With a very high welding point density, and consequentlyseam density, the diffusion bond 25.2 can be produced in the from of aseam 16.2 with virtually uniform seam thickness d over the extent in theadvancing direction.

The seam 16.2 according to FIG. 2 is also of one row. However, with thistype of arrangement of the components 3.2 and 4.2, a two-rowed seamconfiguration is also conceivable. In this case, a second parallel seam16.22 would be arranged at a distance a16 from the seam 16.2. Thissecond seam is represented here in FIG. 2 a by a broken line just toillustrate this possibility, and is preferably produced by means offurther welding electrodes, which are not represented here and arearranged parallel to the welding electrodes 11.2 and 12.2.

FIG. 2 c illustrates a further development according to FIG. 2 a, withthe provision of a welding filler 26.2 in the joining region 5.2. Saidwelding filler here comprises at least the coating of a contact area22.2 or 23.2 in the overlapping region 6.2 of the two components 3.2 and4.2 to be connected to one another, preferably the two mutually facingcontact areas 22.2 and 23.2. The choice of material for the weldingfiller 26.2 and the basic principle of the mode of operation in thiscase correspond to that described in FIG. 1 c.

While a pressure-welding method was assumed in FIGS. 1 a to 1 c forrealizing a diffusion bond 25, FIG. 3 a and 3 b illustrate a furtherpossibility by means of a modified fusion-welding method. Bothcomponents 3.3 and 4.3 have a bevel and the arrangement of the twocomponents 3.3 and 4.3 takes place in this case one over the other witha broad surface area in the region of the bevels, i.e. both in theadvancing direction and transversely to the latter, as represented inFIG. 1 a and 1 b. In the contact region between the two components 3.3and 4.3, in particular the contact areas 22.3 and 23.3, the overlappingregion 6.3 is formed. A TIG welding device is used in this case as thewelding device 1.3. It comprises at least one electrode 21, which isassigned to the overlapping region 6.3 in the joining region 5.3 andpermits an energy input between the two contact areas 22.3 and 23.3 inthe overlapping region 6.3. The two components 3.3 and 4.3 to be weldedto one another are in this case not completely melted during the actualwelding operation, but only the upper region 7.3, 8.3. The melting zoneof the TIG seam 24 is only about 15 to 25% of the sheet thickness of oneof the two components 4.3 or 3.3. Following the production of the TIGseam 24, the latter is mechanically recompacted in a further, secondmethod step by hammering. It is possible here, as represented in FIG. 3b, for this method step to follow on directly after the weldingoperation, in that the energy input introduced at the same timedetermines the temperature for the hammering operation. Here, too, acorresponding device 18.3 is provided for applying local impact loading.This device is arranged downstream of the welding device 1.3 in theadvancing direction. In addition, a device 19 (see FIG. 1 d) for heatingthe diffusion bond 25.3 formed at TIG seam 24 may be arranged upstreamof the device 18.3. Alternatively, a spatial and temporal separationbetween the two method steps is possible, as described for example inFIG. 1 d. The end product is in both eases a permanent integralconnection 2.3.

FIG. 4 a illustrates a metallographic transverse section through thewelded seam of two PtRh10-ODS sheets welded to one another. In thiscase, joining was performed in the first method step by means of rollerseam welding. The final diffusion bond was obtained by hammering. Nowelding filler was used. In the region of the former contact areas ofthe overlapping regions there is scarcely any remaining evidentdifference in microstructure. This is particularly clear in the middlepicture.

FIG. 4 b illustrates a metallographic transverse section through thewelded seam of two PtRh10-ODS metallic components welded to one another.Although joining was performed by means of roller seam welding, thefinal diffusion bond was subsequently obtained by hammer welding. Inthis case, a foil of pure platinum was placed as a welding fillerbetween the materials to be connected to one another in the overlappingregion or joining region. The coarser grain structure in the foilcompared with the fine-grained microstructure of the ODS material isclearly evident.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A method for producing permanent integral connections ofoxide-dispersed metallic materials by welding, comprising: supplying twomaterials or components of the materials to be connected to one another;overlapping the materials or components, one over the other, to form anoverlapping region, including a joining region at the overlappingregion; performing a first welding operation by heating the materials orcomponents at the joining region below the melting temperatures of thematerials or the components without compression whereby the materials orcomponents form, at least partially, a diffusion bond; and performing asubsequent and temporally delayed second welding operation by heatingthe diffusion bond to a temperature below the melting temperature of thematerials or components to be connected, and by mechanicallyrecompacting the diffusion bond.
 2. The method of claim 1, wherein thematerials or components to be connected have respective differentmelting temperatures with one of the materials or components having ahigher melting temperature and the other of the materials or componentshaving a lower melting temperature, the method further comprisingheating the materials to be connected in the joining region to atemperature in a range between 0.6 and 0.9 times the melting temperatureof the material having the lower melting temperature.
 3. The method ofclaim 1, wherein the mechanical recompacting of the diffusion bondoccurs directly downstream and after the welding which forms, at leastpartially, a diffusion bond.
 4. The method of claim 3, wherein the stepof mechanically recompacting the diffusion bond is performed at atemperature corresponding to that of the first welding step.
 5. Themethod of claim 1, wherein the mechanical recompacting is performed at adifferent time and at a different location than the first weldingoperation.
 6. The method of claim 1, wherein the materials or componentsto be connected have respective different melting temperatures with oneof the materials or components having a higher melting temperature andthe other of the materials or components having a lower incitingtemperature; and the heating of the diffusion bond before the mechanicalrecompacting is to a temperature in the range of 0.6 to 0.9 times themelting temperature of the material or component having the lowermelting temperature.
 7. The method of claim 6, wherein the heating ofthe diffusion bond before the mechanical recompacting is by a directcurrent flow.
 8. The method of claim 1, wherein the mechanicalrecompacting is performed by applying a constant impact load to thediffusion bond by hammering on the bond.
 9. The method of claim 8,wherein the diffusion bond has opposite sides corresponding to oppositesides of the connection being formed, and the recompacting is performedby applying the impact load uniformly on both opposite sides of thediffusion bond.
 10. The method of claim 1, wherein the first weldingoperation is performed without a welding filler.
 11. The method of claim1, further comprising arranging a welding filler between the materialsor components to be connected to one another in the joining regionbefore the first welding operation is performed, and performing thefirst welding operation with the welding filler.
 12. The method of claim11, wherein the welding filler comprises at least one noble metal foildisposed between the materials or components to be connected in thejoining region.
 13. The method of claim 12, wherein the noble metal foilis a material more ductile than metal sheet.
 14. The method of claim 12,wherein the noble metal foil has a thickness in the range of 20 μm to200 μm.
 15. The method of claim 12, further comprising arranging two ofthe noble metal foils overlapping one another in the joining region. 16.The method of claim 11, wherein the components or materials to beconnected in the joining region have respective mutually facing contactareas; the method further comprising applying a noble metal coating onthe mutually facing contact areas to be connected in the joining regionwherein the coating defines a welding filler for the first weldingoperation.
 17. The method of claim 1, wherein the welding filler is analloy selected from the group consisting. Pt, Pt—Ir, Pt—Au, Pt—Rh, andcombinations thereof.
 18. The method of claim 1, further comprisingarranging the materials or components in the joining region to define alap joint at the joining region.
 19. The method of claim 1, furthercomprising arranging the materials or components to be connected to oneanother in the joining region so as to form an overlapping regionincluding a parallel joint between the materials or components.
 20. Themethod of claim 1, wherein the materials or components to be connectedto one another each have a bevel in the joining region, the methodfurther comprising arranging the materials or components so that thebevels overlap before the first welding operation is performed.
 21. Themethod of claim 20, wherein the bevels are defined by beveled faceswhich overlap in an overlapping region, and the oxide dispersed metallicmaterials are arranged in one plane with the beveled faces in contactwith each other over their respective entire surface in the overlappingregion.
 22. The method of claim 20, wherein the materials or componentswhen connected at the joining region have a thickness and have a lengthof the bevels, and the length of the bevels corresponds to a range oftwo to five times the thickness of the joined materials or components atthe joining region.
 23. The method of claim 20, wherein the bevels aredefined by respective beveled faces on the materials or components inthe joining region, and at least one of the beveled faces in the joiningregion has an increased surface roughness with respect to other surfaceareas of the components.
 24. The method of claim 23, further comprisingproviding the beveled faces with greater surface roughness duringfabrication of the bevels or during a finishing operation performed onthe beveled faces using an embossing roller.
 25. The method of claim 20,wherein the bevels are defined by respective beveled faces on thematerials or components in the joining region and the entire beveledfaces in the joining region having an increased surface roughness withrespect to other surface areas of the components.
 26. The method ofclaim 23, wherein the roughened regions of the beveled faces have anaverage roughness depth of between 40 μm and 120 μm.
 27. The method ofclaim 1, further comprising connecting oxide-dispersion-strengthenedmaterials at a number of the joining regions which are parallel in aperpendicular sectional plane through the overlapping regions andbetween two of the components by setting the number of joining regionsto be equal to n−1.
 28. The method of claim 1, wherein the overlappingregion provides a plurality of joints of oxide-dispersed metallicmaterial, the method comprising locally bringing the joints into aflowable state one after the other progressively either in an advancingdirection of a welding device for welding or an advancing direction ofthe materials or components to be welded with respect to a weldingdevice; the bringing of the materials or components at the joiningregion into a flowable state comprises uniformly supplying heat at bothsides of the material or component at the overlapping region in a heataffected zone for plastically unifying the materials or components underpressure; the welding being performed such that there are neighboringwelding points produced when individual joints are connected, and thedistance between two neighboring welding joints produced when individualjoints are connected is less than the dimension of a welding point inthe advancing direction.
 29. The method of claim 28, wherein the weldingis performed by a seam-welding method, which produces seam connections,and the welding is performed so that the seam connections are in rows inthe advancing direction.
 30. The method of claim 28, further comprisingwelding points along the welding joint and the welding being performedso that neighboring ones of the welding points of the welding device orthe materials or components form a seam with either no variations orvery small variations in the seam thickness in the advancing direction.31. The method of claim 1, wherein the first welding operation furthercomprises heating the materials or components to bring the joints to aflowable state by providing at least one of energy sources selected fromthe group consisting of electrical energy, ultrasound and induction. 32.The method of claim 31, wherein the first welding operation is performedby inducing at both sides of the materials and components in the joiningregion a heat of fusion using at least one welding electrode, connectedto a source of electric current for a selected time interval, thewelding being produced as a result of the high transition resistance atthe component.
 33. The method of claim 32, further comprisingcontrolling the melting depths on the oxide dispersed metallic materialsas a function of at least one of the current intensity, the rate ofrelative advancement of at least one of the welding electrode and thematerials or components being welded with respect to the other one, andcontact pressure.
 34. The method of claim 32, further comprising using aroller seam-welding method for the resistance welding and usingrotatably mounted rolling electrodes as the welding electrodes on bothsides at the overlapping region, the method further comprising drivingat least one of the electrodes to rotate and causing the electrodes toexert pressure on the materials or components being welded.
 35. Themethod of claim 34, further comprising mounting and adjusting therolling electrodes displaceably with respect to the materials andcomponents to be welded for enabling adjustment of the contact pressure.36. The method of claim 31, further comprising using a TIG weldingmethod modifiable with respect to the energy input to the weldingdevice.
 37. The method of claim 1, wherein the materials or componentsto be welded are of respective different materials.
 38. The method ofclaim 37, wherein the materials or components to be welded consist of anoxide-dispersed material based on Pt-ODS or Pt—Au5-ODS or PtRh10-ODS.39. The method of claim 1, wherein the materials or components to bewelded at least at the joining region comprise materials which are notstrengthened, whereby the welding is of purely fusion-alloy materials orcomponents.
 40. The method of claim 39, wherein the materials orcomponents consist of materials based on Pt, Pt—Au, Pt—Rh or Pt—Ir. 41.The method of claim 1, wherein the materials or components which are tobe welded have different respective thicknesses.
 42. The method of claim1, wherein a combined gravity and overhead position defines the weldingposition of the materials or components at the joint.